The present invention relates to a fuel injection control apparatus of an internal combustion engine where the timing of fuel injection is calculated on the basis of a signal outputted from a crank angle detector.
Japanese Laid-Open Patent Publication No. 2002-303199 discloses a crank angle detector for detecting the rotational angle of the crankshaft of an internal combustion engine, that is to say, the crank angle. This crank angle detector includes a rotor with teeth made of a magnetic body which is attached to the crankshaft, that is to say, a signal rotor, and a magnet pickup coil. A number of teeth are provided on the outer periphery of the signal rotor at equal angular intervals. In addition, a toothless portion is created in a portion of the outer periphery of the signal rotor by leaving out teeth. The toothless portion is used to detect the reference position for the crank angle.
Usually the timing of fuel injection (the time when injection starts and the time when injection is completed) is first set as a crank angle. Next, the tooth portion (reference tooth portion), which is a reference, is set on the basis of this crank angle, and at the same time, the standby period after the point in time when a detection signal corresponding to the above described reference tooth portion is detected and before the point in time when fuel injection starts or is completed is determined. When fuel injection control is carried out, the reference tooth portion is detected by the magnet pickup coil. After that, fuel injection starts or is completed, at the point in time when it is determined that the standby period has elapsed through measurement by a timer.
In addition, the above described standby period changes in accordance with the rotational speed of the crankshaft. Concretely, the rotational speed of the crankshaft is obtained from the length of time between two detected signals which respectively correspond to any two adjacent tooth portions before the reference tooth portion, and the thus obtained rotational speed is regarded as the rotational speed of the crankshaft at that time, and the standby period is determined with the reference tooth portion as the starting point. In the case where the length of time between the detected signals corresponding to two adjacent tooth portions is short, the obtained rotational speed of the crankshaft becomes high, and therefore, the standby period with the reference tooth portion as the starting point also becomes short.
In an internal combustion engine with eight cylinders as those disclosed in Japanese Laid-Open Patent Publication No. 2002-303199 and Japanese Laid-Open Patent Publication No. 2005-315107, the timing interval between one fuel injection and the previous fuel injection corresponds to a crank angle of 90°. Meanwhile, in the case of an internal combustion engine with a relatively small number of cylinders, for example, four cylinders, the timing interval between one fuel injection and the previous fuel injection corresponds to a crank angle of approximately 180°. Accordingly, engines having a greater number of cylinders have a shorter interval between fuel injections. In addition, the number of internal combustion engines in which pilot injection is carried out before the main fuel injection or post injection is carried out after the main injection has been increasing in recent years. In the case where pilot injection or post injection is carried out in an engine having a relatively great number of cylinders, the interval between fuel injections becomes considerably short. Therefore, in cases where the timing of fuel injection is set in the above described manner, a detection signal corresponding to the toothless portion must sometimes be used, when the standby period, which is the base for the calculation of injection timing, is obtained. However, the length of time, which is obtained on the basis of the detection signal corresponding to the toothless portion, is basically longer than the length of time between detection signals corresponding to two adjacent tooth portions, and therefore, the detection signal corresponding to the toothless portion cannot be used as it is.